Anisotropic magnetoresistive (AMR) sensors and techniques for fabricating same

ABSTRACT

Novel anisotropic magneto-resistive (AMR) sensor architectures and techniques for fabricating same are described. In at least one embodiment, an AMR sensor is provided that includes barber pole structures having upper and low metal layers that are formed of different materials. The metal material closer to the AMR element is formed of a material that can be etched using an etching process that does not attack the AMR material. In some other embodiments, AMR sensors having segmented AMR sensing elements are described.

FIELD

Subject matter disclosed herein relates generally to sensors and, moreparticularly, to sensors that include magnetoresistive (MR) elements.

BACKGROUND

Magnetoresistance is the ability of a material to change its electricalresistance when exposed to an external magnetic field. This ability maybe taken advantage of to provide, among other things, sensors fordetecting magnetic field intensity. Anisotropic magnetoresistance (AMR)is a form of magnetoresistance where the change in resistance of amaterial depends upon the angle between the direction of magnetizationand the direction of current flow in the material. Typically, theresistance of an AMR material will be a maximum when the magnetizationof the material is in the same direction as the current. To achievelinear operation in an AMR sensor, an angle may need to be maintainedbetween the direction of magnetization with no external magnetic fieldapplied (i.e., the easy angle) and the current in the AMR element. Mostmodern AMR sensors use “barber pole” structures to provide the desiredcurrent angle. Typically, an angle of around 45 degrees is used.

As with any electrical device, there is a need for new and improved AMRsensor architectures. There is also a need for new techniques forefficiently and/or inexpensively fabricating AMR sensors. Techniques arealso needed for producing AMR sensors that are capable of highperformance operation.

SUMMARY

In accordance with one aspect of the concepts, systems, circuits, andtechniques described herein, an anisotropic magneto-resistive (AMR)sensor comprises: an inter layer dielectric (ILD) surface; an AMRelement above the ILD surface, the AMR element being at least partiallyformed of an AMR material; and a plurality of barber poles above andconductively coupled to the AMR element, wherein each of the barberpoles includes a lower portion formed of a first metal material and anupper portion formed of a second metal material, wherein the first metalmaterial is a material that can be etched using an etching process thatdoes not attack the AMR material of the AMR element.

In one embodiment, the first metal material includes a titanium compoundand the second metal material includes an aluminum compound.

In one embodiment, the first metal material includes titanium-tungsten(TiW) and the second metal material includes aluminum-copper (AlCu).

In accordance with another aspect of the concepts, systems, circuits,and techniques described herein, a method for fabricating an anisotropicmagneto-resistive (AMR) sensor, comprises: providing an inter layerdielectric (ILD) surface; forming a stack over the ILD surface, thestack having an AMR element formed of an AMR material, a first metallayer above the AMR element, and a second metal layer above the firstmetal layer, wherein the first and second metal layers are formed ofdifferent metal materials; applying a mask over the stack to definebarber poles; etching the stack using a first etching process andstopping before reaching the AMR element; and etching the stack using asecond etching process, after etching the stack using the first etchingprocess, wherein etching the stack using the second etching processincludes stopping upon or after reaching the AMR element.

In one embodiment, the second etching process is less damaging to theAMR material of the AMR element than is the first etching process.

In one embodiment, the first metal layer comprises a titanium compoundand the second metal layer comprises an aluminum compound.

In one embodiment, the first metal layer comprises titanium-tungsten(TiW) and the second metal layer comprises aluminum-copper (AlCu).

In one embodiment, the first etching process includes a dry etch using achlorinated chemistry and the second etching process includes a dry etchusing a fluorinated chemistry.

In one embodiment, the first etching process uses a solution includingat least one of BCl3, CL2, and CCl4; and the second etching process usesa solution including at least one of CF4, CHF3, and NF3.

In one embodiment, the first etching process includes a dry etch using achlorinated chemistry and the second etching process includes a wet etchusing a solution including hydrogen peroxide (H₂O₂) and water (H₂O).

In one embodiment, etching the stack using the first etching process isstopped upon or after reaching the first metal layer.

In accordance with a further aspect of the concepts, systems, circuits,and techniques described herein, an anisotropic magneto-resistive (AMR)sensor comprises: a plurality of metallic elements on a first layer; anda plurality of separate anisotropic magneto-resistive (AMR) elementsegments on a second layer; wherein the plurality of metallic elementsare conductively coupled to the plurality of AMR element segments sothat a current applied to the AMR sensor will flow through the pluralityof metallic elements and the plurality of AMR element segments in analternating fashion.

In one embodiment, the first and second layers are separated from oneanother by at least one layer of dielectric material; and the pluralityof metallic elements are conductively coupled to the plurality of AMRelement segments using via connections.

In one embodiment, the AMR sensor has a longitudinal direction; and thevia connections are located so that, during sensor operation, currentwill flow within the plurality of AMR element segments in a directionthat is at an acute angle to the longitudinal direction of the AMRsensor.

In one embodiment, the via connections are arranged in groups havingorientations that are different from the longitudinal direction of theAMR sensor.

In one embodiment, the first and second layers are abutting; and theplurality of metallic elements are conductively coupled to the pluralityof AMR element segments by direct conductive contact.

In one embodiment, the plurality of metallic elements are disposed abovean inter layer dielectric (ILD) surface of the AMR sensor, and theplurality of AMR element segments are disposed above the plurality ofmetallic elements; wherein the AMR sensor further includes a passivationlayer above the plurality of AMR element segments to protect the AMRsensor from external environmental conditions.

In accordance with still another aspect of the concepts, systems,circuits, and techniques described herein, a method for fabricating ananisotropic magneto-resistive (AMR) sensor, comprises: forming aplurality of metallic elements on a first layer to serve as barber polesfor the AMR sensor, forming a plurality of separate AMR element segmentson a second layer; and providing conductive connections between theplurality of metallic elements and the plurality of separate AMR elementsegments so that a current applied to the AMR sensor will flow throughthe plurality of metallic elements and the plurality of AMR elementsegments in an alternating fashion during sensor operation.

In one embodiment, providing conductive connections between theplurality of metallic elements and the plurality of separate AMR elementsegments includes forming via connections between the plurality of AMRelement segments and the plurality of metallic elements.

In one embodiment, forming via connections includes forming groups ofvia connections in an orientation that supports current flow at adesired angle within the separate AMR element segments during sensoroperation.

In one embodiment, forming via connections is performed after formingthe plurality of metallic elements and forming the plurality of separateAMR element segments.

In one embodiment, forming the plurality of AMR element segments isperformed after forming the plurality of metallic elements.

In one embodiment, forming the plurality of AMR element segments isperformed before forming the plurality of metallic elements.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing features may be more fully understood from the followingdescription of the drawings in which:

FIG. 1 is a top view of a conventional anisotropic magnetoresistive(AMR) sensor having metallic barber poles disposed on top of anunderlying film of AMR material;

FIGS. 2 and 3 are sectional side views of exemplary AMR sensorarchitectures having AMR elements disposed above barber pole elements inaccordance with various embodiments;

FIG. 4 is a sectional side view of an exemplary AMR sensor architecturehaving an AMR element disposed above barber pole elements that does notuse planarization in accordance with an embodiment;

FIG. 5 is a flowchart illustrating an exemplary method for fabricatingan AMR sensor having an AMR element disposed above barber pole elementsin accordance with an embodiment;

FIG. 6 is a sectional side view of an exemplary AMR sensor that includesmultiple capping layers in accordance with an embodiment;

FIG. 7 is a sectional side view of an exemplary AMR sensor that includesa single capping layer in accordance with an embodiment;

FIG. 8 is a flowchart illustrating an exemplary method for use infabricating an AMR sensor having at least one capping layer inaccordance with an embodiment;

FIGS. 9A-9E are sectional side views illustrating various stages in anexemplary process for fabricating an AMR sensor in accordance with anembodiment;

FIG. 10 is a flowchart illustrating a method for fabricating an AMRsensor using two different etching processes in accordance with anembodiment;

FIGS. 11 and 12 are a top view and a sectional side view, respectively,of an AMR sensor that uses a segmented AMR element in accordance with anembodiment; and

FIG. 13 is a flowchart illustrating a method for fabricating an AMRsensor having a segmented AMR element in accordance with an embodiment.

DETAILED DESCRIPTION

FIG. 1 is a top view of an anisotropic magnetoresistive (AMR) sensor 10having metallic barber poles 12, 14, 16, 18, 20 disposed on top of anunderlying film 22 of a magnetic material having the AMR property (whichwill be referred to hereinafter as an AMR material). The barber poles12, 14, 16, 18, 20 are formed of aluminum or other suitable conductorand are oriented at an angle of 45 degrees with respect to alongitudinal direction 24 of the sensor. During sensor operation, a testcurrent I_(r) is applied to the sensor 10 to measure changes in anelectrical resistance of the film 22 of AMR material to sense anexternal magnetic field. Typically, a number of AMR sensor elements maybe implemented in a bridge configuration to facilitate the measurementof the resistance changes. In other embodiments, the segments of thebarber poles 12 and 20 are not included and contact is made to the AMRlayer in those areas.

The current I_(r) may be applied to a first barber pole 12 of the sensor10. Because of the resistivity of the barber poles 12, 14, 16, 18, 20 ismuch lower than that of the AMR material, the current will flow throughthe barber poles 12, 14, 16, 18, 20 when it can, and will flow throughthe underlying AMR material 22 in the gaps between the barber poles 12,14, 16, 18, 20. In addition, the differences in resistivity between thematerials will cause the current in the gap regions to flow through theAMR material at an angle dictated by the angle of the barber poles 12,14, 16, 18, 20. This is because the current will take the shortest routethrough the higher resistivity material (i.e., perpendicular to theedges of the barber poles 12, 14, 16, 18, 20). It is due to the magneticfield being measured that the route is changed and thus the resistanceis increased. As shown in FIG. 1, the current I through the AMR materialflows at a 45 degree angle to the longitudinal direction 24 of thesensor. The current eventually exits the sensor 10 at the last barberpole 20. In general, the barber poles need to be made of a material withlow enough resistance (or resistivity) to effectively redistribute thecurrent flow.

In a typical implementation, the underlying film 22 of AMR material maybe formed so that a magnetization vector with no applied magnetic field(i.e., the easy axis) is in a longitudinal direction with respect to thesensor 10 (i.e., along a long axis of the sensor 10 or the AMR element).The sensor may then be used, for example, to sense changing magneticfields in a transverse direction. Other arrangements may alternativelybe used.

In conventional AMR sensors, the barber poles are implemented on top ofthe AMR element, as described above. It was found that this approachpresented a potential for contamination in some fabrication processflows. For example, in some conventional process flows, etches performedduring fabrication are required to stop on the AMR material (e.g.,permalloy (NiFe), etc.) of the AMR element, which exposes the etchingtool to NiFe contamination. In conceiving some of the features,techniques, and structures described herein, it was determined thatfabrication efficiencies and cost reductions could be achieved byforming the AMR element above (or after) the barber poles during sensorfabrication. As indicated above, the AMR elements of AMR sensors areoften formed from a material known as permalloy, which is an alloy ofnickel and iron. In general, iron is a material that is not easy to dealwith in a clean room fabrication environment. By forming the AMR elementabove the barber pole structures, the lower portion of the AMR sensorcan be generated using a standard device fabrication process (e.g., aCMOS, BiCMOS, or similar standardized process). The AMR element can thenbe added using a different process (e.g., in a different fabricationenvironment, equipment, or clean room) without having to expose theoriginal fabrication environment to NiFe or another AMR material.

FIG. 2 is a sectional side view of an exemplary AMR sensor 30 inaccordance with an embodiment. It should be appreciated that thestructures illustrated in FIG. 2, and in other figures described herein,may not be to scale. That is, one or more dimensions within the variousfigures may be exaggerated to increase clarity and facilitateunderstanding. As shown, the AMR sensor 30 may be formed on top of aninter layer dielectric (ILD) 32 or substrate. As used herein, the terms“ILD,” “ILD layer,” and “ILD surface” encompass any surface ofdielectric material within a device including a substrate of dielectricmaterial or layers higher than the substrate. The ILD layer may beformed of any of a variety of different dielectric materials including,for example, SiO₂, SiN_(x)N_(y) (nitride), Al₂O₃ (or other aluminumoxide compounds), and many others. A metal layer 34 may be deposited onthe ILD surface and formed into metal elements to serve as barber poles36 a, 36 b, 36 c, 36 d, 36 e. Any of a variety of different techniquesmay be used to shape the barber poles 36 a, 36 b, 36 c, 36 d, 36 eincluding, for example, deposition, photolithography, and etch; or seedlayer deposition, patterning (photolithography), and electroplating,and/or others. Although illustrated in FIG. 2 with 5 barber poleelements 36 a, 36 b, 36 c, 36 d, 36 e, it should be appreciated that anynumber of elements greater than 2 may be used in differentimplementations. The metal layer 34 may be formed of aluminum, copper,gold, or any other metal or metal alloy having the desiredcharacteristics to serve as barber pole elements.

Although not shown in FIG. 2, the barber poles 36 a, 36 b, 36 c, 36 d,36 e may be oriented at a fixed angle (e.g., 45 degrees, etc.) withrespect to a longitudinal direction (x) of the sensor 30 (as viewed fromabove). Alternatively, the barber poles 36 a, 36 b, 36 c, 36 d, 36 e maybe oriented at a variable angle, where the edge of the barber polechanges angle across the AMR width. In some embodiments, the regions 38a, 38 b, 38 c, 38 d between the barber poles 36 a, 36 b, 36 c, 36 d, 36e may be filled with a dielectric material after the barber poles areformed. An upper surface of metal layer 34 with the dielectric materialin the regions may then be planarized using any of a variety ofplanarization techniques.

After the barber poles 36 a, 36 b, 36 c, 36 d, 36 e have been formed, anAMR element 40 may next be formed above metal layer 34. The AMR element40 may be formed of any of variety of AMR materials, the most common ofwhich is NiFe. As described previously, in some implementations, theformation of the AMR element 40 (as well as subsequent processing steps)may be performed in a different processing environment or clean roomfrom the above described fabrication steps. In one approach, a film ofAMR material may first be deposited as a sheet or layer over an uppersurface of metal layer 34. A mask may then be applied to the AMR filmand the film may be etched into the desired shape of AMR element 40. Insome cases, the mask may be a photoresist mask, while in other cases ahard mask such as an oxide or a nitride may be deposited and thenpatterned with a photoresist or similar material. After the AMR element40 has been formed, a layer of passivation 42 may be applied over thetop and sides of the AMR element 40 to, among other things, protect theAMR element 40 from an external environment. Metallic contacts 44 a, 44b may be formed to provide external connection points on the AMR sensor30 to, for example, allow measurement circuitry to be coupled thereto.In other embodiments, these contacts connect to other areas of theintegrated circuit. As shown, the metallic contacts 44 a, 44 b may eachbe conductively coupled to corresponding ones of the barber poleelements 36 a, 36 e. In other embodiments, alternative structures may beprovided to permit connection to the sensor (e.g., tungsten plugs toprovide connection from below, etc.). In still other embodiments, thepads for bonding may be provided elsewhere in the integrated circuit.

In the AMR sensor 30 of FIG. 2, some or all of the barber pole elements36 a, 36 b, 36 c, 36 d, 36 e may be arranged in an orientation that willresult in a desired current flow direction within the AMR element 40during sensor operation. In some embodiments, this current flowdirection may within a range of approximately 30 to 60 degrees withrespect to the long axis (or the longitudinal axis) of the AMR element40. In at least one embodiment, this current flow direction is nominally45 degrees with respect to the long axis of the AMR element 40.

FIG. 3 is a sectional side view of an exemplary AMR sensor 50 inaccordance with an embodiment. AMR sensor 50 is similar to AMR sensor 30of FIG. 2, except one or more additional layers 48 exist between metallayer 34 and AMR element 40. For example, in one implementation, layer48 may include a layer of hard metal (e.g., tungsten (W), titanium (Ti),titanium nitride (TiN), etc.) on top of metal layer 34 to facilitatesubsequent planarization (e.g., polishing, etc.). If used, the hardmetal layer may be applied before the barber pole elements are patternedon metal layer 34. The material used for the hard metal layer must havean appropriate conductivity for use between the barber pole elements ofmetal layer 34 and AMR element 40.

In addition to, or as an alternative to, the hard metal layer, layer 48may also include a seed layer to facilitate uniform growth of the AMRfilm above metal layer 34. The seed layer may be formed from any ofvariety of different materials including, for example, copper (Cu), gold(Au), and/or others. If used, the seed layer would preferably be appliedafter planarization. In some embodiments, an adhesion layer may precedethe seed layer to improve the mechanical adhesion of the seed layer tothe underlying layer. The adhesion layer may include, but is not limitedto, a titanium or chromium layer having a thickness in the range ofapproximately 10 to 500 Angstroms.

Layer 48 may also, or alternatively, include a diffusion barrier toprevent diffusion of material between metal layer 34 and AMR element 40(e.g., diffusion between an aluminum layer and a NiFe layer, etc.). Insome embodiments, a single metal layer may be used that serves as both adiffusion barrier and a hard metal layer. The material that is used inthese layers will typically depend on the materials used in metal layer34 and AMR element 40. When aluminum is used in the metal layer 34 andNiFe is used in AMR element 40, materials such as tungsten (W), titanium(Ti), titanium nitride (TiN), etc. may be used as both a diffusionbarrier and a hard metal layer.

In some embodiments, non-metallic materials may be used as ahard/diffusion barrier. For example, in at least one embodiment, a verythin layer of alumina (Al₂O₃) or a similar dielectric material may beused. The alumina layer must be thin enough to allow electron tunnelingbetween the barber poles and the AMR element (e.g., less than 3 to 8Angstroms in thickness, and maybe less than 1 Angstrom). Such layers mayprovide an increased level of hardness to facilitate planarization.

FIG. 4 is a sectional side view of an exemplary AMR sensor 60 inaccordance with still another embodiment. The AMR sensor 60 of FIG. 3may be easier to construct than the previously described embodiments asone or more processing steps associated with those embodiments have beeneliminated. As before, barber poles 36 a, 36 b, 36 c, 36 d, 36 e areformed on a metal layer 34 above an ILD layer 32. However, instead offilling in the regions between the barber pole elements 36 a, 36 b, 36c, 36 d, 36 e with dielectric material and then planarizing, the AMRmaterial may be deposited over the barber pole elements 36 a, 36 b, 36c, 36 d, 36 e and allowed to fill the regions. The resulting AMR filmmay then be patterned to a desired size and shape. This technique mayrequire the AMR film layer to be thicker than the metal layer 34associated with the barber poles. As shown, because the AMR film wasallowed to fill in the regions, an upper surface 64 of the AMR element62 may not be smooth (e.g., it may have depressions or other distortionscorresponding to the regions below). In some embodiments, the uppersurface 64 of the AMR element 62 may be planarized at this point.However, in other embodiments, as shown in FIG. 4, the upper surface 64of the AMR element 62 may be left unplanarized and a passivation layer42 may be applied to the unplanarized element. Contact pads 44 a, 44 bmay then be added to the sensor 60 as described previously.

In some embodiments, one or more capping layers may be used within anAMR sensor to protect some materials within the sensor from othermaterials. One or more capping layers may also serve as an etch stopduring sensor fabrication to avoid the need to etch down to one or morematerials that may be problematic during sensor fabrication. As will bedescribed in greater detail, in at least one embodiment, an AMR sensorhaving one or more capping layers may be fabricated using a simplifiedprocess whereby all layers of the sensor element and the barber polesare deposited before any patterning is performed. Patterning may then beperformed in two successive stages: a first stage to form the shape ofthe AMR element and a second stage to form the shape of the barber poleelements.

FIG. 5 is a flowchart illustrating an exemplary method 90 forfabricating an AMR sensor in accordance with an embodiment. The method90 may be used to fabricate sensors such as, for example, thoseillustrated in FIGS. 2, 3, and 4, as well as other AMR sensors. An interlayer dielectric (ILD) surface is first provided upon which the AMRsensor will be built (block 92). A plurality of metallic elements maynext be formed above the ILD surface to serve as barber pole conductorsfor the AMR sensor (block 94). In some embodiments, the formation of themetallic elements may include the deposition of one or more of a hardmetal layer, a diffusion barrier, or a seed layer above the metallicelements. One or more layers of metal may be deposited on the ILDsurface and the layers may then be masked and etched to form themetallic elements. As described previously, the metallic elements may beoriented at an angle (e.g., 45 degrees) to a longitudinal directionassociated with the sensor being fabricated.

An AMR element may next be formed above the plurality of metallicelements (block 96). In some embodiments, the regions between themetallic elements may be filled with a dielectric material and aplanarization process may then be used to planarize an upper surface ofthe metallic elements before the AMR element is formed. In otherembodiments, the AMR element may be formed without first filling in theregions and planarizing. In these embodiments, the AMR element mayextend down to the ILD surface below. To form the AMR element, a film ofAMR material may first be deposited over the metallic elements.Patterning may then be used to shape the AMR film into the desiredelement shape.

After the AMR element has been formed, a passivation process may be usedto enclose the AMR element, and possibly the metallic elements, toprotect them from an external environment (block 98). In embodimentswhere the regions between the metallic elements were not filled in withdielectric material, the upper layer of the AMR element may be uneven.In some embodiments, the passivation may be applied directly to theuneven AMR element without first planarizing the upper surface thereof.In other embodiments, the upper surface of the AMR element may beplanarized before the passivation is applied.

In some embodiments, metallic contact pads may next be formed to provideexternal connection points for the AMR sensor (block 100). These contactpads may be used, for example, to connect external measurement circuitryto the AMR sensor. The metallic contact pads may be formed through thepassivation material to contact corresponding ones of the metallicelements. In other embodiments, other techniques may be used to provideexternal connection to the AMR element.

FIG. 6 is a sectional side view of an exemplary AMR sensor 70 thatincludes multiple capping layers in accordance with an embodiment. Asshown, the AMR sensor 70 may be formed above, for example, an ILD layer72. In some embodiments, tungsten plugs 74 a, 74 b may be provided inthe ILD layer 72 to allow connection to the sensor 70 from below. TheAMR sensor 70 may have an AMR element 78 formed above the ILD layer 72.The AMR element 78 may have a seed layer 76 below it. The seed layer 76may be provided to, for example, facilitate growth of an AMR film fromwhich the AMR element 78 is formed. In some implementations, a seedlayer may not be present.

A first capping layer 80 may be formed over the AMR element 78. Onepurpose for the first capping layer 80 may be to protect other materialswithin the AMR sensor 70 from the AMR material of the AMR element 78.Another possible purpose may be to serve as an etch stop duringformation of the barber poles of the sensor 70 so that the etch does notextend through to the AMR material (which can cause contamination). Thefirst capping layer 80 may be formed of any material that is capable ofprotecting other materials in the AMR sensor 70, at least to someextent, from the AMR material of AMR sensor 78. Capping materials thatmay be used include, for example, tantalum (Ta), tungsten (W), titanium(Ti), titanium nitride (TiN), and others. If used, the capping layer 80should be thin so that it does not increase the resistance to the barberpole structures and thereby prevent a significant portion of the totalcurrent in the AMR layer 78 from flowing into the barber poles.Alternatively, a more conductive capping layer 80 can be used such asruthenium (Ru), where the conductivity is high enough as not to pose thesame restriction of thinness as noted above. As shown in FIG. 6, evenwith capping layer 80, there may be some exposure to the AMR material ofelement 78 on the sides of the element. However, this exposure willtypically only be a small percentage of the exposure that would existwithout the capping layer 80.

With reference to FIG. 6, barber poles 88 may be formed over the AMRelement 78. The barber poles 88 may each have a lower portion 82 formedof a metal material such as, for example, copper, copper-aluminum,aluminum, or some other metal. The barber poles 88 may each also have anupper portion to serve as a second capping layer 84 to protect othermaterials in the sensor 70 from the metal of lower portion 82. Thesecond capping layer 84 may be formed of the same material as, or adifferent material from, the first capping layer 80 (e.g., tantalum(Ta), tungsten (W), titanium (Ti), titanium nitride (TiN), and/orothers).

In at least one embodiment, to form the AMR sensor 70 of FIG. 6, theseed layer 76, a layer of AMR material, the first capping layer 80, ametal layer, and the second capping layer 84 may all be deposited beforeany patterning is done. The patterning may then be performed in twosteps. In at least one embodiment, ion beam etching may be used toperform the patterning in both steps, although other techniques orcombinations of techniques may alternatively be used. The firstpatterning step is performed to form the desired shape of the AMRelement 78. The second patterning step is performed to form the desiredshape of the barber poles 88. During sensor fabrication, the firstpatterning step may stop on the ILD layer 72 or some other dielectriclayer. The second patterning step may stop at or within the firstcapping layer 80. In this manner, the AMR material is not exposed fromabove, thereby reducing the risk of contamination. Masks may be formedfor each patterning step and then stripped after each patterning iscomplete. In some cases, masks may remain if they do not interfere witha subsequent step in the process and then mask materials may be etchedat the same time if appropriate before moving on to a subsequent processstep.

After the barber poles 88 have been formed, a passivation material 86may be applied over the AMR sensor 70 to protect the sensor fromexternal environmental conditions. In some embodiments, as shown in FIG.7, an AMR sensor similar to that of FIG. 6 may be fabricated without thefirst capping layer 80. In such embodiments, the etch process to formthe barber poles will extend down to the AMR material of the AMR sensor78.

FIG. 8 is a flowchart illustrating an exemplary method 110 for use infabricating an AMR sensor in accordance with an embodiment. The method110 may be used to fabricate, for example, the sensor 70 of FIG. 6 orsimilar sensors. As illustrated, an ILD surface may first be provided(block 112). An optional adhesion and/or seed layer may then be formedon the ILD surface to facilitate the deposition of an AMR film (block114). An AMR film may then be formed on the seed layer (or the ILDsurface if a seed layer is not provided) (block 116). A first cappinglayer may next be deposited over the AMR film (block 118). In someembodiments, a first capping layer is not provided.

A metal layer (e.g., a layer of copper or another metal or metal alloy)may next be formed above the layer of AMR material (block 120). A secondcapping layer may then be formed above the metal layer (block 122). Afirst patterning step may then be performed to form the desired shape ofthe AMR element (block 124). A second patterning step may then beperformed to form the barber poles over the AMR element (block 126). Thefirst and second patterning steps may use the same patterning process ordifferent processes. In at least one implementation, photolithographyand then ion beam etching is used for both steps. An optional hard maskmay be deposited before photolithography and then patterned afterphotolithography before the ion beam etch step. If a first capping layeris used, the second patterning step to form the barber poles may bestopped within the first capping layer before it reaches the AMRelement. If a first capping layer is not used, the second patterningstep may extend down to the AMR element. After the barber poles havebeen formed, a passivation process may be used to cover the barber polesand the AMR material with a passivation material (block 128). Metalliccontacts may then be formed through the passivation material to providean electrical connection to the AMR sensor or some other connectiontechnique may be used (e.g., a connection from below using tungstenplugs, etc.).

FIGS. 9A-9E are sectional side views illustrating various stages in anexemplary process for fabricating an AMR sensor in accordance with anembodiment. With reference to FIG. 9A, the process may begin with an ILDlayer 130 with or without tungsten plugs 132, 134. A layer of AMRmaterial 136 (e.g., NiFe, etc.) may then be deposited upon the ILD layer130 using any known deposition process. In some embodiments, a seedlayer may first be formed on the ILD layer 130 before the AMR layer 136is deposited (although this is not performed in every embodiment). Afirst metal layer 138 and a second metal layer 140 may then be depositedover the layer of AMR material 136. As will be described in greaterdetail, the materials used for the first and second metal layers 138,140 may be selected based upon the etching processes and chemistriesthat work well with the two materials. In some embodiments, the firstmetal layer 138 may be formed from titanium tungsten (TiW), or someother titanium based compound, and the second metal layer 140 may beformed from aluminum copper (AlCu), or some other aluminum basedcompound (e.g., Al, AlSi, etc.). Other materials may be used for thefirst and second metal layers 138, 140 in other embodiments. In someembodiments, an adhesion layer and/or diffusion barrier may be depositedbetween the layer of AMR material 136 and the first metal layer 138 toimprove adhesion and/or reduce diffusion (although these layers are notused in every embodiment).

Referring now to FIG. 9B, the AMR layer 136 and the first and secondmetal layers 138, 140 may next be patterned into an AMR element 136having first and second metal layers 138, 140 above. Any of a variety ofdifferent patterning techniques may be used to form the AMR element 136.With reference to FIG. 9C, a layer of photo-resist 142 or other maskmaterial may be formed over the AMR element 136 and the first and secondmetal layers 138, 140. The photo-resist layer 142 may then be formedinto a mask having the pattern of the barber poles of the AMR sensorbeing fabricated. A first etching process and process chemistry may thenbe used to etch through the second metal layer 140 to a point at a topboundary of or within (but not all the way through) the first metallayer 138, as shown in FIG. 9C. A second etching process and processchemistry may then be used to etch the rest of the way through the firstmetal layer 138 (and any intervening layers) to the AMR element 136.

In at least one embodiment, the second etching process will be a processthat does not significantly attack the AMR material of the AMR element136 such that the AMR film will not function as the desired magneticfield sensor. As such, the material used for the first metal layer 138may be a material that works well with the selected etching process. Asdescribed above, in some embodiments, titanium tungsten (TiW) or someother titanium based compound may be used for the first metal layer 138.In these embodiments, a dry etch process using a fluorinated chemistrysuch as, for example, CF₄, CHF₃, SF₆, or others may be used for thesecond etching process as these chemistries do not attack magneticfilms, such as NiFe. As an alternative, in some embodiments, a wet etchprocess may be used for the second etching process using a chemistrysuch as, for example, hydrogen peroxide/water (H₂O₂/H₂O) or phosphoricacetic nitric (PAN). Other processes are also possible for the secondetching process. The first etching process used to etch through thesecond metal layer 140 can be a process that does attack the AMRmaterial as this process will not reach the AMR element 136 duringfabrication. This process may include, for example, a dry etch processusing a chlorinated chemistry such as, for example, BCl₃ or Cl₂. Thesechemistries work well with aluminum and aluminum compounds as well asother metals. Other processes may alternatively be used for the firstetching process.

After the second etching process has completed, the photo-resist 142 maybe stripped to compete the formation of the barber poles. FIG. 9D showsthe resulting sensor with barber poles 146 after the photo-resist 142has been stripped. In some cases, it may be desirable to deposit a hardmask and pattern the hard mask (e.g., if a wet etching process is usedfor the second etching process), and it may be desirable to strip thephoto-resist 142 before the second etching process. As shown in FIG. 9E,after the barber poles 146 have been formed, a coating of passivation148 may be applied to the sensor to protect it from, for example, anexterior environment. Any of various techniques may be used to providean external electrical connection to the sensor.

FIG. 10 is a flowchart illustrating a method 160 for fabricating an AMRsensor in accordance with an embodiment. The method 160 may be used tofabricate, for example, the sensor shown in FIG. 9E as well as other AMRsensors. An ILD surface may first be provided upon which the sensor willbe formed (block 162). A seed layer may then be formed on the ILDsurface (block 164). In some embodiments, a seed layer may not be used.An AMR element having first and second metal layers above it may then beformed over the ILD surface (block 166). The first and second metallayers will be used to form the barber poles of the AMR sensor. In atleast one embodiment, the first metal layer is formed oftitanium-tungsten (TiW) or another titanium compound and the secondmetal layer is formed of aluminum-copper (AlCu) or another aluminumcompound. Other metal materials may alternatively be used. In oneapproach, the AMR element with the first and second metal layers may beformed by first depositing a layer of AMR material over the ILD surfaceand then depositing first and second metal layers over the layer of AMRmaterial. The three layers may then be patterned together into thedesired shape of the AMR element. Other techniques may alternatively beused to form the AMR element.

A mask may next be applied over the second metal layer to form thebarber poles of the sensor (block 168). A first etching process is thenused to etch through the second metal layer (block 170). The firstetching process may be stopped once the first metal layer is reached, orsomewhere within the first metal layer, but will not be permitted toproceed all the way through to the AMR material of the AMR element Asecond etching process may then be used to finish the etch through tothe AMR material of the AMR element (block 172). The second etchingprocess will be a process that is less deleterious to the AMR materialthan the first etching process would be. In at least one embodiment, thefirst etching process is a dry etch using a chlorinated chemistry andthe second etching process is a dry process using a fluorinatedchemistry. In another approach, the first etching process is a dry etchusing a chlorinated chemistry and the second process is a wet etchingprocess using, for example, a hydrogen peroxide-water chemistry. Otherprocess combinations may alternatively be used.

In conventional AMR sensors, barber pole structures are typically formedin abutting conductive relation to an underlying AMR element. In someembodiments described below, separation exists between barber poleconductors and AMR material. In these embodiments, via connections orother structures for providing interlayer conductive coupling may beused to couple the barber poles to the AMR material. In addition, insome embodiments, instead of using a single continuous AMR element as inconventional sensors, a segmented element is used that has multipleseparate AMR element sections that are interconnected with one anotherthrough the barber pole conductors.

FIGS. 11 and 12 are a top view and a sectional side view, respectively,of an AMR sensor 190 that uses a segmented AMR element in accordancewith an embodiment. As shown in FIGS. 11 and 12, the AMR sensor 190includes a number of barber pole conductor elements 192 a, 192 b, 192 c,192 d, 192 e on a first layer and a number of AMR element segments 194a, 194 b, 194 c, 194 d on a second layer that is above the first layer.The barber pole conductor elements 192 a, 192 b, 192 c, 192 d, 192 e maybe formed on an ILD layer 200. In the illustrated embodiment, the firstand second layers are separated from one another by one or moreintervening dielectric layers 196. Via connections 198 are used toprovide conductive coupling between the barber pole conductor elements192 a, 192 b, 192 c, 192 d, 192 e and the AMR element segments 194 a,194 b, 194 c, 194 d. Techniques for forming via connections betweenconductive layers are known in the art. Although illustrated with fourAMR element segments 194 a, 194 b, 194 c, 194 d in FIGS. 11 and 12, itshould be appreciated that any number of AMR element segments (i.e., twoor more) may be used in other segmented AMR element embodiments. Inaddition, in at least one implementation, the finished sensor 190 mayinclude a passivation layer 202 covering the AMR element segments 194 a,194 b, 194 c, 194 d and dielectric layer 196.

As shown in FIG. 12, the barber pole conductor elements 192 a, 192 b,192 c, 192 d, 192 e and the AMR element segments 194 a, 194 b, 194 c,194 d may be interconnected so that a current applied to a barber poleelement at one end of the sensor (e.g., element 192 a) will flow throughall of the barber pole conductor elements 192 a, 192 b, 192 c, 192 d,192 e and all of the AMR element segments 194 a, 194 b, 194 c, 194 d inan alternating fashion (i.e., barber pole element, AMR element segment,barber pole element, AMR element segment, and so on) before emergingfrom a barber pole element at an opposite end of the sensor (e.g.,element 192 e). In addition, the locations and orientation of the viaconnections 198 and the conductivities of the associated materials, maybe selected so that the current I will flow through the AMR elementsegments 194 a, 194 b, 194 c, 194 d at an angle to the easy axis thereof(e.g., a 45 degree angle in the illustrated embodiment). The AMR elementsegments 194 a, 194 b, 194 c, 194 d may be magnetized so that the easyaxis of each of the segments aligns with the longitudinal direction ofthe sensor (although this might not be the case in some embodiments).

With reference to FIG. 11, the via connections 198 may be formed withingroups (e.g., in rows, etc.) that form a 45 degree angle with respect toa longitudinal direction of the sensor 190. If the combined resistanceof the barber pole elements 192 a, 192 b, 192 c, 192 d, 192 e and thecorresponding via connections 198 is low enough with respect to theresistance of the AMR element segments 194 a, 194 b, 194 c, 194 d, thenthe current (I) will flow within the AMR element segments 194 a, 194 b,194 c, 194 d at a 45 degree angle, as shown in FIG. 11. For example, inone possible implementation, the resistance of each AMR element segmentmay be around 20 Ohms, the resistance of each barber pole element may bearound 0.1 Ohms, and the resistance of each group of via connections maybe around 0.05 Ohms. Thus, the combined resistance of one barber poleelement and two via groups will be substantially less than theresistance of one corresponding AMR element segment. In this scenario,the current flow will occur within the AMR element segments at thedesired angle. Other resistance scenarios may be used in otherembodiments. It should be appreciated that both the number and the sizeof the via connections used in a particular implementation may beselected so that an appropriate via resistance is achieved to supportcurrent flow at the desired angle in the AMR element segments. In somealternative embodiments, the AMR material layer 194 is not cut betweenthe via connection areas.

In the embodiment illustrated in FIGS. 11 and 12, the barber poleelements 192 a, 192 b, 192 c, 192 d, 192 e are implemented below the AMRelement segments 194 a, 194 b, 194 c, 194 d. As described previously,this arrangement may provide various benefits related to, for example,the prevention of contamination during the fabrication process. In someembodiments, however, an AMR sensor having a segmented AMR element maybe provided with the barber pole elements located above the AMR elementsegments.

In the embodiment of FIG. 11, the barber pole elements 192 a, 192 b, 192c, 192 d, 192 e and the AMR element segments 194 a, 194 b, 194 c, 194 dare shown as having edges that also form 45 degree angles to thelongitudinal direction of the sensor 190. However, this is not the casein every embodiment. That is, it is the angle associated with the viaconnections that will establish the current angle within the AMR elementsegments 194 a, 194 b, 194 c, 194 d and not the outer shape of thebarber pole elements 192 a, 192 b, 192 c, 192 d, 192 e and the AMRelement segments 194 a, 194 b, 194 c, 194 d. The edges of these elementsmay be angled, however, so that a more compact sensor can be achieved.It should be appreciated that the density of the vias may have to beadjusted in a particular design to achieve a viable resistance scenarioin the sensor 190.

In at least one embodiment, an AMR sensor is provided that uses asegmented AMR element, but does not use via connections between the AMRsensor segments and the corresponding barber pole elements. That is, theAMR sensor segments and the barber pole elements are formed in anabutting, conductively coupled relation to one another with nointervening dielectric layer (although there could be one or moreintervening conductive layers, such as a seed layer, a diffusionbarrier, etc.). For example, with reference to FIG. 12, in onealternative arrangement, the AMR element segments 194 a, 194 b, 194 c,194 d may be disposed directly above the barber pole elements 192 a, 192b, 192 c, 192 d, 192 e, with no dielectric layer 196 in between. Asdescribed previous, the regions between the barber pole elements 192 a,192 b, 192 c, 192 d, 192 e may, in some embodiments, be partially orfully filled with dielectric material before the AMR element segments194 a, 194 b, 194 c, 194 d are formed. Planarization may also beperformed before the AMR element segments 194 a, 194 b, 194 c, 194 d areformed in some implementations. In the above-described arrangement, thecurrent flow within the AMR element segments 194 a, 194 b, 194 c, 194 dwill still be at the desired angle with respect to the easy axis. Theshapes of the barber pole elements 192 a, 192 b, 192 c, 192 d, 192 e andthe AMR element segments 194 a, 194 b, 194 c, 194 d will be moreimportant in this arrangement, however. That is, the edges of thesestructures will have to be angled to provide the desired currentdirection.

FIG. 13 is a flowchart illustrating a method 210 for fabricating an AMRsensor having a segmented AMR element in accordance with an embodiment.A plurality of metallic elements are formed on a first layer to serve asbarber pole elements for the AMR sensor (block 212). A plurality ofseparate AMR element segments are provided on a second layer (block214). Conductive coupling is provided between the plurality of metallicelements and the plurality of AMR element segments so that a currentapplied to the AMR sensor will flow through the plurality of metallicelements and the plurality of AMR element segments in an alternatingfashion during sensor operation. In different embodiments, the metallicelements may be formed either before or after the AMR element segments.In some embodiments, the first layer and the second layer may beseparated from one another by at least one dielectric layer. In theseembodiments, via connections may be used to provide the conductivecoupling between the elements. In other embodiments, the conductivecoupling may be provided by forming the plurality of metallic elementsand the plurality of AMR element segments in an abutting, conductiverelationship to one another.

In some embodiments, the via connections that are used to provide theconductive coupling between the elements are arranged in groups havingan orientation that supports current flow at a desired angle within theAMR element segments, during sensor operation. The angle may be, forexample, an angle of 45 degrees (or approximately 45 degrees) withrespect to an easy angle of the AMR element segments (although otherangles may be used in other implementations). The via connections willtypically be formed after the formation of the plurality of metallicelements and the formation of the plurality of AMR element segments. Inone implementation, for example, the plurality of metallic elements mayfirst be formed on an ILD layer. One or more other dielectric layers maythen be deposited over the plurality of metallic elements. The AMRelement segments may then be formed over the intervening dielectriclayer(s). The via connections may then be formed to conductively couplethe metallic elements to the AMR element segments. Techniques forforming via connections in desired locations are well known in the art.In at least one implementation, after the metallic elements have beenconductively coupled to the AMR element segments, a passivation layermay be applied over the AMR sensor to protect the sensor from externalenvironmental conditions.

In the discussion above, various exemplary embodiments have beendescribed. It will be apparent to those of ordinary skill in the artthat modifications and variations may be made to these exemplaryembodiments without departing from the spirit and scope of theinvention. These modifications and variations are considered to bewithin the purview and scope of the invention and the appended claims.It will also be apparent to those of ordinary skill in the art that thedisclosed embodiments, although different, are not necessarily mutuallyexclusive. That is, one or more features, structures, or characteristicsdescribed herein in connection with one embodiment may be incorporatedinto one or more other embodiments to form new embodiments withoutdeparting from the spirit and scope of the invention. Similarly, thelocation or arrangement of individual elements within each disclosedembodiment may be modified without departing from the spirit and scopeof the invention. All publications and references cited herein areexpressly incorporated herein by reference in their entirety.

What is claimed is:
 1. An anisotropic magneto-resistive (AMR) sensorcomprising: an inter layer dielectric (ILD) surface; an AMR elementabove the ILD surface, the AMR element being at least partially formedof an AMR material; and a plurality of barber poles above andconductively coupled to the AMR element, wherein each of the barberpoles includes a lower portion formed of a first metal material and anupper portion formed of a second metal material, wherein the first metalmaterial is at least partially etched using an etching process that doesnot attack the AMR material of the AMR element.
 2. The AMR sensor ofclaim 1, wherein: the first metal material includes a titanium compoundand the second metal material includes an aluminum compound.
 3. The AMRsensor of claim 1, wherein: the first metal material includestitanium-tungsten (TiW) and the second metal material includesaluminum-copper (AlCu).
 4. A method for fabricating an anisotropicmagneto-resistive (AMR) sensor, comprising: providing an inter layerdielectric (ILD) surface; forming a stack over the ILD surface, thestack having an AMR element formed of an AMR material, a first metallayer above the AMR element, and a second metal layer above the firstmetal layer, wherein the first and second metal layers are formed ofdifferent metal materials; applying a mask over the stack to definebarber poles; etching the stack using a first etching process andstopping before reaching the AMR element; and etching the stack using asecond etching process, after etching the stack using the first etchingprocess, wherein etching the stack using the second etching processincludes stopping upon or after reaching the AMR element.
 5. The methodof claim 4, wherein: the second etching process is less damaging to theAMR material of the AMR element than is the first etching process. 6.The method of claim 4, wherein: the first metal layer comprises atitanium compound and the second metal layer comprises an aluminumcompound.
 7. The method of claim 4, wherein: the first metal layercomprises titanium-tungsten (TiW) and the second metal layer comprisesaluminum-copper (AlCu).
 8. The method of claim 4, wherein: the firstetching process includes a dry etch using a chlorinated chemistry andthe second etching process includes a dry etch using a fluorinatedchemistry.
 9. The method of claim 8, wherein: the first etching processuses a solution including at least one of: BCl3, CL2, and CCl4; and thesecond etching process uses a solution including at least one of: CF4,CHF3, and NF3.
 10. The method of claim 4, wherein: the first etchingprocess includes a dry etch using a chlorinated chemistry and the secondetching process includes a wet etch using a solution including hydrogenperoxide (H₂O₂) and water (H₂O).
 11. The method of claim 4, wherein:etching the stack using the first etching process is stopped upon orafter reaching the first metal layer.
 12. An anisotropicmagneto-resistive (AMR) sensor comprising: a plurality of metallicelements on a first layer; and a plurality of separate anisotropicmagneto-resistive (AMR) element segments on a second layer; wherein theplurality of metallic elements are conductively coupled to the pluralityof AMR element segments so that a current applied to the AMR sensor willflow through the plurality of metallic elements and the plurality of AMRelement segments in an alternating fashion.
 13. The AMR sensor of claim12, wherein: the first and second layers are separated from one anotherby at least one layer of dielectric material; and the plurality ofmetallic elements are conductively coupled to the plurality of AMRelement segments using via connections.
 14. The AMR sensor of claim 13,wherein: the AMR sensor has a longitudinal direction; and the viaconnections are located so that, during sensor operation, current willflow within the plurality of AMR element segments in a direction that isat an acute angle to the longitudinal direction of the AMR sensor. 15.The AMR sensor of claim 12, wherein: the first and second layers areabutting; and the plurality of metallic elements are conductivelycoupled to the plurality of AMR element segments by direct conductivecontact.
 16. The AMR sensor of claim 12, wherein: the plurality ofmetallic elements are disposed above an inter layer dielectric (ILD)surface of the AMR sensor; and the plurality of AMR element segments aredisposed above the plurality of metallic elements; wherein the AMRsensor further includes a passivation layer above the plurality of AMRelement segments to protect the AMR sensor from external environmentalconditions.
 17. A method for fabricating an anisotropicmagneto-resistive (AMR) sensor, comprising: forming a plurality ofmetallic elements on a first layer to serve as barber poles for the AMRsensor; forming a plurality of separate AMR element segments on a secondlayer; and providing conductive connections between the plurality ofmetallic elements and the plurality of separate AMR element segments sothat a current applied to the AMR sensor will flow through the pluralityof metallic elements and the plurality of AMR element segments in analternating fashion during sensor operation.
 18. The method of claim 17,wherein: providing conductive connections between the plurality ofmetallic elements and the plurality of separate AMR element segmentsincludes forming via connections between the plurality of AMR elementsegments and the plurality of metallic elements.
 19. The method of claim18, wherein: forming via connections includes forming groups of viaconnections in an orientation that supports current flow at a desiredangle within the separate AMR element segments during sensor operation.20. The method of claim 17, wherein: forming the plurality of AMRelement segments is performed before forming the plurality of metallicelements.